Optical fiber now is in widespread use as communication media. Typically, an optical fiber includes a glassy core which may be on the order of 8 .mu.m for single mode transmission or about 62.5 .mu.m for multimode transmission and a cladding. About the cladding is disposed one or more layers of a coating material. The coating material or materials is used to protect the optical fiber. When an optical fiber is terminated by a ferrule for example, it becomes necessary to remove the coating material or materials from an end portion of the optical fiber.
An optical fiber cable includes a sheath system which protects an optical fiber, which extends along the longitudinal axis of the cable and which serves as an optical communications path. Not only does the sheath system protect the glass fiber, but also it provides the cable with flexibility and with suitable tensile, flexural and impact strength. For multi-fiber cables, the sheath system may include several extruded layers of plastic as well as one or more metallic shields disposed between elements of the sheath system.
Optical fibers of a cable may be terminated in any one of several ways. Each fiber may be terminated by a connector widely known as a biconic connector. Such a connector is disclosed in U.S. Pat. No. 4,512,630 which issued on Apr. 23, 1985 in the name of P. K. Runge. Another connector is one referred to as an ST.RTM. connector, ST being a registered trademark of AT&T. Also useable is an array connector which terminates a planar array of optical fibers between two chips.
Single fiber cables also are well known in the art. They also may be terminated with biconic connector plugs or ST connectors. Generally, a single fiber cable includes a coated optical fiber which is enclosed in a buffer layer. The buffer layer typically is made of an extruded plastic material such as polyvinyl chloride. Such a single optical fiber cable generally is referred to as a buffered optical fiber. Over the buffer layer in another embodiment may be disposed a yarn which provides strength for the cable. The yarn may be an aramid fibrous yarn and is usually served in a helical fashion about an advancing buffered optical fiber. An outer jacket generally is extruded about the yarn.
Buffered optical fibers are used, for example, in central offices to connect cables to optical transmission apparatus. Also, buffered optical fibers may be used widely in buildings. For example, they may be used in riser cables which may comprise anywhere from two to thirty-six buffered fibers. Riser cables are used to interconnect cables which enter building equipment rooms to wiring closets on upper floors. Further, buffered optical fibers may be used in plenums which extend from the riser closets on each floor to satellite closets or directly to equipment and for connecting the equipment to plenum cables.
A still further use of buffered optical fibers is in the local area network. Therein, distribution cables extend from distribution cabinetry to drop closures and thence to terminal locations. Buffered fibers appear to be the choice for inclusion in those cables which extend from distribution cabinetry to each home, for example.
It has been found that buffered fiber cables are somewhat difficult to strip for connectorization. That is, difficulties have been encountered in the removal of the buffer layer from the coated optical fiber. This is particularly true in those instances where it is desired to expose a substantial length of optical fiber for particular connectorization arrangements.
The prior art dislcoses the use of a release agent for buffered optical fiber. In U.S. Pat. No. 4,072,400, a buffered optical waveguide fiber includes an optical waveguide fiber which is coated with a glass protective coating with a release agent coating applied over the glass protective coating. A protective layer of a thermoplastic synthetic resinous material surrounding the fibers is disposed over the release agent. As disclosed in the aforementioned U.S. Pat. No. 4,072,400, the release agent material may be any suitable lubricant such as silicone oil, petroleum lubricant, a layer of colloidal graphite, talc or the like.
Presently, when it is desired to remove the buffer layer, a stripping tool including opposed knife blades is manipulated to cause the blades to cut through the buffer layer. Afterwards, forces are applied to the tool to cause the buffer layer to be pulled from the optical fiber. However, because of the adhesion of the buffer layer to the coating material, the forces required to remove the buffer layer may cause the fiber to break, particularly when trying to remove about one inch of the buffer layer to expose sufficient optical fiber for termination purposes. Once the fiber is broken, the craftsperson must begin the process anew.
This problem has been overcome by removing the one inch length of buffering in incremental steps of one-sixteenth inch each, for example. As should be apparent, this is a time consuming procedure and alternatives have been sought after.
Another problem relates to the removal of the buffer layer and the underlying coating material from the optical fiber in a single operation. There are instances when not only is it desired to remove a length of the buffer layer from the underlying coated optical fiber but also the coating layer or layers as well. In fact in some installations, it becomes necessary to remove both the buffer layer and the coating layer or layers from a length of the underlying optical fiber and then to remove only the buffer layer from an adjacent portion of the buffered optical fiber. As should be apparent, the buffered optical fiber which is sought after must include provisions to facilitate the removal of the buffer layer or both the buffer layer and the coating materials from the optical fiber.
Of course, although the sought-after cable must be one in which the buffer layer or the buffer layer and the coating material must be able to be removed somewhat easily, the cable must also have other properties. For example, there must be sufficient adhesion between the buffer layer and the underlying coating material to maintain the buffer layer in place during normal use.
What is needed and what seemingly is not provided by the prior art is a buffered optical fiber which is relatively small in size. Further, the sought-after buffered optical fiber should be one in which the covering buffer material has a controlled coupling to an underlying coated optical fiber so that it may be removed easily to expose the optical fiber for connectorization. Still further, the sought-after buffered optial fiber should be one in which reasonable lengths of both the covering buffer layer and the coating layer or layers of the optical fiber may be removed desirably at the same time in a single operation without causing fracture of the fiber.